Intaglio printing presses are widely used in security printing for printing security documents, especially banknotes. Prior art intaglio printing presses are for instance disclosed in Swiss Patent No. CH 477 293, European Patent Applications Nos. EP 0 091 709 A1, EP 0 406 157 A1, EP0 415 881 A2, EP 0 563 007 A1, EP 0 873 866 A1, EP 1 602 483 A1, and International Applications Nos. WO 01/54904 A1, WO 03/047862 A1, WO 2004/026580 A1, WO 2005/118294 A1.
FIGS. 1 and 2 schematically illustrate a known intaglio printing press configuration with an intaglio printing unit configuration similar to that disclosed in European Patent Application No. EP 0 091 709 A1.
FIG. 1 shows a sheet-fed intaglio printing press 1 comprising, as is usual in the art, a sheet feeder 2 for feeding sheets to be printed, an intaglio printing unit 3 for printing the sheets, and a sheet delivery unit 4 for collecting the freshly-printed sheets. The intaglio printing unit 3 typically includes an impression cylinder 7, a plate cylinder 8 carrying intaglio printing plates (in this example, the plate cylinder 8 is a three-segment cylinder carrying three intaglio printing plates 8a, 8b, 8c—FIG. 2), an inking system 9 for inking the surface of the intaglio printing plates 8a, 8b, 8c carried by the plate cylinder 8 and an ink wiping system 10 for wiping the inked surface of the intaglio printing plates 8a, 8b, 8c carried by the plate cylinder 8 prior to printing of the sheets.
The sheets are fed from the sheet feeder 2 onto a feeder table and then onto the impression cylinder 7. The sheets are then carried by the impression cylinder 7 to the printing nip formed by the contact location between the impression cylinder 7 and the plate cylinder 8 where intaglio printing is performed. Once printed, the sheets are transferred from the impression cylinder 7 to a sheet transporting system 11 in order to be delivered to the delivery unit 4. The sheet transporting system 11 conventionally comprises an endless conveying system with a pair of endless chains driving a plurality of spaced-apart gripper bars for holding a leading edge of the sheets (the freshly-printed side of the sheets being oriented downwards on their way to the delivery unit 4), sheets being transferred in succession from the impression cylinder 7 to a corresponding one of the gripper bars.
During their transport to the sheet delivery unit 4, the freshly printed sheets are preferably inspected by an optical inspection system 5. In the illustrated example, the optical inspection system 5 is advantageously disposed along the path of the sheet transporting system 11, right after the printing unit 3. Such an optical inspection system 5 is already known in the art and does not need to be described in detail. Examples of optical inspection systems adapted for use as optical inspection system 5 in the intaglio printing press of FIG. 1 are for instance described in International Applications Nos. WO 97/36813 A1, WO 97/37329 A1 and WO 03/070465 A1. Such inspection systems are in particular marketed by the Applicant under the product designation NotaSave®.
Before delivery, the printed sheets are preferably transported in front of a drying unit 6 disposed after the inspection system 5 along the transport path of the sheet transporting system 11. Drying could possibly be performed prior to the optical inspection of the sheets.
FIG. 2 is a schematic view of the intaglio printing unit 3 of the intaglio printing press 1 of FIG. 1. As already mentioned, the intaglio printing unit 3 basically includes the impression cylinder 7, the plate cylinder 8 with its intaglio printing plates 8a, 8b, 8c, the inking system 9 and the ink wiping system 10.
The inking system 9 comprises in this example four inking devices, three of which cooperate with a common ink-collecting cylinder or Orlof cylinder 9.5 (here a two-segment cylinder) that contacts the plate cylinder 8. The fourth inking device is disposed so as to directly contact the surface of the plate cylinder 8. It will be understood that the illustrated inking system 9 is accordingly adapted for both indirect and direct inking of the plate cylinder 8. The inking devices cooperating with the ink-collecting cylinder 9.5 each include an ink duct 9.10, 9.20, 9.30 cooperating in this example with a pair of inking rollers 9.11, 9.21 and 9.31, respectively. Each pair of inking rollers 9.11, 9.21, 9.31 in turn inks a corresponding chablon cylinder (also designated as selective inking cylinder) 9.13, 9,23, 9.33, respectively, which is in contact with the ink-collecting cylinder 9.5. As for the fourth inking device, it includes an ink duct 9.40, an additional inking roller 9.44, a pair of inking rollers 9.41 and a chablon cylinder 9.43, this latter cylinder being in contact with the plate cylinder 8. The additional ink roller 9.44 is necessary in this latter case as the fourth inking device 9.4 is used to directly ink the surface of the plate cylinder 8 which rotates in opposite direction as compared to the ink-collecting cylinder 9.5. As is usual in the art, the surface of the chablon cylinders 9.13, 9.23, 9.33 and 9.43 is structured so as to exhibit raised portions corresponding to the areas of the intaglio printing plates 8a, 8b, 8c intended to receive the inks in the corresponding colours supplied by the respective inking devices.
The ink wiping system 10, on the other hand, typically comprises a wiping tank 10.1 (which is movable towards and away from the plate cylinder 8), a wiping roller 10.2 supported on and partly located in the wiping tank and contacting the plate cylinder 8, cleaning means 10.3 for removing wiped ink residues from the surface of the wiping roller 10.2 using a wiping solution that is sprayed or otherwise applied onto the surface of the wiping roller 10.2, and a drying blade 10.4 contacting the surface of the wiping roller 10.2 for removing wiping solution residues from the surface of the wiping roller 10.2. The wiping roller 10.2 can typically be removed from the wiping tank 10.1 during maintenance operations using a crane 12 (see FIG. 1).
A particularly suitable solution for an ink wiping system comprising a wiping roller is disclosed in International Application No. WO 2007/116353 A1 (corresponding to EP 1 844 930 A1) which is incorporated herein by reference in its entirety.
The most common solution used for wiping excess ink from the surface of an intaglio printing cylinder is, as discussed hereinabove, to use a wiping roller assembly that rotates in the same direction as the intaglio printing cylinder. Such wiping roller assembly typically consists of a cylinder base made commonly of metal and bearing at least one layer of wiping material, preferably a layer of polymer material such as PVC material. The structure and manufacture of such wiping rollers is for instance disclosed in U.S. Pat. Nos 3,785,286, 3,900,595,4,054,685 and International Applications Nos. WO 2007/031925 A2, WO 2007/031927 A2, WO 2007/034362 A2 which are incorporated herein by reference.
As mentioned above, such wiping roller is supported on and partly located in a wiping tank for rotation against the surface of the intaglio printing cylinder, the surface of the wiping roller being cleaned from wiped ink residues using a wiping solution that is typically sprayed onto the surface of the wiping roller.
With such a known solution, the wiping pressure between the intaglio printing cylinder and the wiping roller is adjusted by playing with the position of the axis of rotation of the wiping roller with respect to the axis of rotation of the intaglio printing cylinder. This is typically achieved by using two adjusting rods or hydraulic cylinders acting on the two ends of the wiping roller, for instance through eccentric bearings. Adjustment mechanisms for adjusting the wiping pressure between a wiping roller and an intaglio printing cylinder are for instance disclosed in European Patent Applications Nos. EP 0 475 890 A1, EP 0 526 398 A1, and U.S. Pat. Nos. 2,987,993, 3,762,319.
These adjustment mechanisms are however not entirely satisfactory as the ability to adjust the wiping pressure along the contact portion between the wiping roller and the intaglio printing cylinder is limited by the fact that one can only play with the position of the axis of rotation of the wiping roller with respect to the intaglio printing cylinder. It is therefore difficult to ensure that the wiping pressure is adequate or substantially uniform over the whole length of the contact portion between the wiping roller and the intaglio printing cylinder. This furthermore leads to a non-uniform wear of the surface of the wiping roller. An improved solution is thus required.
Furthermore, maintenance operations of the known ink wiping systems are time-consuming as the wiping roller is a relatively heavy component to manipulate, which typically necessitates the use of a crane to remove the wiping roller from the wiping tank (as for instance illustrated in FIGS. 1 and 2).
Besides the above ink wiping systems that make use of a wiping roller as wiping medium, it is also known to wipe excess ink from the surface of a rotatable intaglio printing plate by means of scraper blade mechanisms and/or wiping webs, such as paper webs. An ink wiping system for an intaglio printing press using a combination of a scraper blade mechanism and of wiping webs is for instance disclosed in U.S. Pat. No. 4,240,347 (which corresponds to GB 2 065 561). An ink wiping system for an intaglio printing press using only wiping webs is disclosed in U.S. Pat. Nos. 1,927,056 and 3,888,172.
According to the solutions described in U.S. Pat. Nos. 1,927,056, 3,888,172 and 4,240,347, the wiping web which acts as wiping medium is pressed against the surface of the intaglio printing cylinder by means of a pressing pad or shoe that extends parallel to the axis of rotation of the intaglio printing cylinder. As described more particularly in U.S. Pat. No. 4,240,347, the wiping pressure between the wiping web and the intaglio printing cylinder is adjusted by acting on the two ends of the pressing pad or shoe. Such solutions thus exhibit basically the same problems as the known ink wiping systems which make use of wiping rollers, namely a lack of ability to properly control and adjust the wiping pressure between the wiping medium and the intaglio printing cylinder over the whole length of the contact portion between the wiping medium and the intaglio printing cylinder.